Coring device



Feb 13, 1951 D. M. SMITH 2,541,785

CORING DEVICE Filed Aug. 22, 1946 3 Sheets-Sheet 1 29A @Nigel IN VENTOR. DONALD M. SMITH BY JMJ/@ ATTORNEY Feb. 13, 1951 D, M, SMITH2,541,785

CORING DEVICE Filed Aug. 22, 1946 3 Sheets-Sheet 2 F/G. 4 /l F/6.5 l/

INVENTOR. DONALD M. SMITH BY UWM/ v Arme/ver Feb. E3, 195i D. M. SMH-H2,54L785 CORING DEVICE Filed Aug. 22, 1946 5 Sheets-Sheet 3 Ff@ Ff@ NPatented Feb. 13, 1951 CORING DEVICE Donald M. Smith, Long Beach,Calif., assignor to The Texas Company, New York, N. Y., a corporation ofDelaware Application August 22, 1946, Serial N o. 692,165

(Cl. Z55-1.4)

9 Claims.

This invention is concerned with coring in bore holes and provides novelapparatus to the end that cores may be taken in rotary drillingoperations and the like without contamination of the core and withoutloss of fluid therefrom.

In recent years, increasing attention has been paidv to core analysis inoil well drilling and the like. Data obtained from cores taken in suchdrilling are used in evaluation of oil reserves, in estimating theproductivity and ultimate production of oil sands, in planning oil fielddevelopment programs and for several other purposes. Heretofore, thedata obtainedin many coring operations has been misleading due toerraticcontamination of the cores by drilling fluids and t loss, prior toanalysis, of fluids originally contained in the cores.

There is a distinct need for a coring device which will permit thetaking of a core on the bottom of a hole without contamination of thecor (either in the coring operation per se or in bringing the core tothe surface and thence to thelaboratory) 'and without the loss offormation pressure with consequent expulsion of the major portion ofliquid and gas from the core. y -As a result of my investigations, Ihave developed a core barrel apparatus of the pressure type (i. e. onein which the coring tube or barrel is; pressed downwardly into theformation to be sampled) so constructed that contamination of the sampleduring the coring operation is prevented'in large measure, the samplebeing sealed immediately after it is taken from the bottom of the hole,so that any fluid in the core may be brought to the surface within thebarrel at formation pressure and thus retained.

rIhe apparatus of my invention results in more accurate coreinformation, with the result that yinterpretation of the data taken fromthe cores is likewise more accurate and permits more'nearly correctevaluation of oil field properties, better estimates of reserves andmore accurate location of oil-water interfaces within an oil producingformation to the end that there may be improved recovery therefrom bygas or water injection. To be more specific, the 4pressure core barrelof my invention gives superior results in the determination of reservoircontent, in the location of gas caps and oil producing formations, andin the determination of the content of the gas cap.

1 n With pressure-type core barrels heretofore available, the cores havebeen taken while surrounded by drilling fluid. When these cores areremoved from the hole, the volume of the cores represents in many casesonly 25% of the volume under pressure within the core barrel, theremaining 75%f' being drilling fluid. As a result, the measurement ofoil contained in the core is reasonably ace' curate, but the amount ofwater is distorted due to the invasion of drilling fluid. This problemis c. TheV prevention of most of the contamination"` of and loss fromcores which has heretofore" occurred, since nearly all cf the volumewithin the sealed core barrel is occupiedby the sample" itself; thedrilling uid is excluded from the cor-l ing zone during the coringoperation; andthe sample is sealed at formation pressure in the bot-'tom of the hole. f

In essence, my invention contemplates the come` bination in apparatusfor taking a core from thef bottom of a drill hole, which comprises acore barrel fastened to the bottom of a drill stemv in alignmenttherewith and open at the lower end with a cutting edge that is driveninto the formation by the weight of the stem, together with eans forclosing the bottom or cutting end of the barrel while it contains thecore and is in the bottom of the hole, so that a sample may be sealed inthe barrel at the formation pressure and withdrawn in its originalcondition. ,v In its preferred form, the apparatus comprises', a mandrelmountable on the bottom of the drill stem in alignment therewith, ashell or sleeve slid-' ably mounted upon the mandrel, a core barrelmounted on the bottom of the mandrel, with an open lower cutting end,and a closure member adapted to close the lower end of the core barrelwhen the mandrel is slid upward with respect to the sleeve. -f

If desired, the mandrel and sleeve may be held in fixed positioninitially by a shear pin or other rupturable means which permitsdisengagement of mandrel and sleeve when weight of the drill stem isrested on the mandrel in the bottom of the well.

It is preferable to provide at least two core barrels with equivalentclosure means so that duplicate samples may be taken from the formalftion being tested.

In the preferred form of the apparatus, the top of the core barrel isopen, and a sealing plugis provided within the barrel which is slidableflipJ 3 ward therein under the force of the sample being cut. Forexample, the plug'may slide upward to an apertured seat so as to drivedrilling fluid or the like upwardly out of the core barrel and keep itout of contact with the sample.

The apparatus should be provided with means, preferably actuated throughthe rotation of the mandrel, ifor vcomp'resz'sing the closure meansagainst the bottom of the core barrel after the sample is taken, thusassuring a tight seal. One preferred form of clamping means comprises asealing nut of non-circular section mounted a corresponding longitudinalborerin the mandrel. The sealing nut is threaded on a boltwhich'be'ar'sagainst the closure means. By rotating the mandrel, the sealing nutdraws the bolt upward with respect to the core barrel and presses the'closure means (say a cap) tight against the bottom. Lf desired, thesealing nut -may be mounted within a wrench sleeve which is'of circularoutside cross section, 'this sleeve 'in 'turn being mounted in acircular bore in "the mandrel and held in positin bye. shear pin lor thelike. When adequate clamping pressure has been 'eXeited by the bolt,the'shear ypin ruptures and prevents damage to the core barrel andthe'rest 'ofthe assembly.

It is desirable to provide shoulders on the mandrel 'andial's'o "onthesleeve to limit `the 'relatv longitudinal sliding movement of these twom'enbe'r's and to prevent 'the sleeve from sliding onf the bottom of themandrel. Y

'The closure Ymeans for sealing thebottom of the core barrel preferablyis 'a "cap or cup mountd'nth'e sleeve and rotatable 'onan axis parallel(aild Ypreferably coaxial) to that v'of sleeve 'and mandrel. Preferablythe cap or cup is mounted on" a 'yoke 'which is spring actuated. In theinitial position assumed by the apparatus inthe hle, the closure meansprevented from swinging over Vvthe end of the core barrel by the corebarrel. itself. When the core barrel and `man drel are pulled upward'with vrespfec'zt to the sleeve after 'the sample is taken, 'the springforces "the c'prt swing underneath the core barrel, after which'rotation of the 'drill stem, with consequent rotation 'of the mandrel,causes the 'sealing nut toturn o ii the center bolt and pull thec'uptight 'gans't 'the bottom of the" core barrel. nt the Sametime, 'the'sealing plug is "pushed upwardly inV 'the "core barrel tight 'againstits lseat. `This preserves formation pressure in the "core barrel.

'Preferably 'the bolt works through an 'upper yoke attached 'tb 'the"core bai-rel and a lower yoke `attached to the 4'sea'l'ir'ig cup. Asthe 'nut Ltightened on the bolt, the ykes are Yforced twrd each other,squeezing the "ends of `the barrel between the'n 'and sealing both ends;the upper end by pushing core and plug against its seat, the lower endwith'the cup, This assembly Vis'le'tacha'ble from the apparatus and maybe removed in toto for transport to the laboratory,

' thus assuring that the core is delivered .ior analy'sis vat formationpressure. d

Y'I'flie invention willebe understood more thoroughly in the light ofthe following detailed description of a presently preferred form of theapparatus, taken in conjunction with the accompanying drawings in whicheFig. -1 .is a sectional elevation of the coring device in position inthe bottom of a borehole just before the core cutting operation.; y

Fig. v2 is la sectional elevation of the vapparatus of Fig. 1 .justafter the cores Vhave been out; Y y

Fig. 3 is a cross-sectional plan through the Fig. Y'lis 4across sectiontaken along the line p 'lf--l of Fig. 4 showing the shear pins attachingmandrel to wrench sleeve;

Fi'g-.`-8 a crosssection taken along the line 8-8 of Fig. l showing theshear pins which 'initially hold the mandrel in fixed relation to Fig. 9'is "an `enlarged' fragmentary cross-"sectional `elevation vof the topof one or the boring tubes or barreIs showing 'the manner in which it issealed;

Fig. 11 is a cross-'sectional elevation 'or the sealing cup of Fig. 10'taken along 'the line l'l-'l'i' of this'gure. I` In essence, 'theapparatus "illustrated by 'the figures comprises a mandrel l0 'adaptedt'ofbe fastened by a conventional 'tool j'oi'n't on the v'bute-y tom ofa rotary drill Astem 1|. The Amandre1- slides man outer sleeve l2,"after a 'rst set 'of Shear 'pins 'l IA, HB 'haveub'tured (s'ee Fig.'1); The outer sleeve or shell ha'sa removable bottoni disc threadedv'or 'otherwise fastened therein'. The mandrely is cylin'dric'alin crosssectionand carries anru'pper'beveled shoulder 13, 'which sli es' downtomate "with a lower shoulder II4 `on "the sleeve. The mandrel has aninner 'shoulder l5 which 'prevents the "outer sleeve fromslidin'g ol thelower end ofthe mandrel.

Within'the mandrel iS a concentric 'infi' ye linuricai bore Lin which "a'wrench' sleeve' lie/*is slidablyidisposed. This v'wrench 'sleeve is "offoute' side cylindrical VVcro'ss Jsection.' but has an inside tube ofhexagonal cross section 'within'which slides 'a right hand 'sealing'nutl that is 'threaded on 'ajcenter bolt i8. "sealing mit ispre;vented-from 'coming on the upper end of the center 'bolt by mea'nsoi 'a'left hand lock' ymit le; Until the final sealing operation, the'wrenchSI''V 'iS 'rigidly fst'ld -inside the vnlall'rfl fby a pair of shear.pins v^2'0, 20A "(se'e Fig.' 'l A'and Fig."7).

An upper `yoke 2l 'is mounted rigidly on .the bottomy of the mandrel andcar-ries a pair of c'oretubes o r barrels 722, 2"2. The function of theupper'yoke, which connects the upper par-ts of the Vcoring assembly, isto transmit the Vsealin g Y.pressure Vvfrom the vsealing nut to the-core tubes. It is rigidly but detachably mounted on the mandrel.

AThe core barrels are disposed `opposite eaother with their axes:parallel to that of ythe center bolt. The bottom edges of the twobarrels are ibeveled to afsharp `edge -to .permit penetrae tion of thelformation to be sampled, land the bore of each barrel is somewhatlarger in lSits, upper-section so that it tends to retain and extractthe core from the 4formation. The coring tubes vare attached vrigidlytothe drill Jstem through the upper yoke and the mandrel so that theentire weight of drill collars and pipes may be put on the coring tubesto push them into the formation to be sampled, as shown in Fig. 2.

The bottom of the sleeve is provided with a pair of cylindrical holes23, 23A to permit the passage of the coring tubes to the bottom of theshell into the formation. (See Fig. 4.)

The apparatus is provided with a lower yoke 24 effectively mounted onthe axis of the sleeve and rotatable around the lower portion of thecenter bolt. The lower yoke carries a pair of sealing cups 25, 25A whichare rotated to seal thebottom of the coring tubes as describedhereinafter. The center bolt passes through both yokes.

The respective coring tubes are provided with sealing plugs 26, 26A.Atthe beginning of the coring operation, as shown in Fig. 1, these plugsare located in the bottoms of the tubes. As the cores are cut, the plugsare pushed to the top of theirfcoring tubes by the cores.

Referring to Fig. 9, the plugs are equipped with packing rings 21, 28which bear against the inside of the coring tubes and provide a lateralseal. The top end of each coring tube has an open bore 29 connectingwith side outlets 29A in the upper yoke 2I through which mud or othermaterial may be expelled. Each coring tube is provided with an annularsoft metal seal 30 just below the outlet bore, and the sealing plug isprovided with an annular knife edge 3| which bears against the soft seatand seals the top of the coring tube in one of the later phases oftheoperation as described hereinafter.r Each sealing plug is providedwith a valve 32 which is closed by the core itself when it pushes thesealing plug to the top of the coring tube. This valve permitsaccidentally entrapped fluid to be ejected. The valves in the sealingplugs are simple affairs comprising a seat 32A and a frusto-conicalclosure member 32B, which is mounted on the lower end of a stem 32C thatslides in a vertical bore in the top of the plug.

AThe'sealing plug is in two parts, an upper portion 33 and a lowerportion 34. The lower portion may be tightened against the upper portionbylmeans of anut 35 in order to squeeze the packing rings outwardly.

, A retaining nut 36 is screwed on the bottom of the center bolt whichpasses through a rotationvbearing 31 mounted concentrically on the`bottom of the sleeve.

shown particularly in Figs. 3 and 4, the lower yoke tends to be rotatedby means of a spiral spring 38 placed around the collar 4I in a recessin the lower yoke. The Spring, however, cannot move the sealing cupsinto the sealing position until the coring tubes have been Withdrawnupwardly, as shown in Fig. 4.

The sleeve or'shell serves four functions. It prevents the clogging ofthe coring assembly. Its shoulders prevent vertical motion when the endof desired movement is reached. After the core has been cut and thedrill string is lifted, the weight of the sleeve causes the lower partof the coring assembly t0 remain stationary until the sealing cups haveslipped into position under the coring tube, as shown in Fig. 4. Whenthe drill string is rotated to tighten the sealing nut on the upperyoke, the outer shell prevents rotation of the center bolt, beingassisted in this action by two short sh tail blades 4D, 40A on itsbottom. It may be noted that the center bolt is free to s lide relativeto the upper coring assembly, but is rigidly connected to the outershell I2. Its func- 6 tion is to force the coring tubes into the sealingcups and hold the assembly under pressure when it is brought out of thehole.

As already indicated, the sealing cups are actuated by the spiral springlocated in a recess in the lower yoke. The spring is fastened to acollar,

4I on the center bolt, which in turn is attached to the bolt by a shearpin (not shown). The spring reacts yagainst the lower yoke and alignsthe sealing cups with the coring tubes after the samples have been cut.

The sealing cups have extended lips on one side of their upper edge inorder to hold the cups in alignment with the coring tubes against thetension of the spiral spring. Soft metal,` discs 43A, 43B in the bottomof'the cups bear against the cutting edge of the coring tubes when theassembly is sealed. (See Figs. 4, 5 and 11.)

The operation of the apparatus is as -fo1lows:.

The initial position of theapparatus justbegfore the cores are cut isshown in Fig. 1. As shown in this ligure, the center bolt has beenrotated counterclockwise until the sealing nut has impinged against thelocknut at the top of the bolt. This prevents further rotation of thecenter bolt and provides the spiral springwitha stop against which toworkl in moving the sealing cups at a later stage in the operation. Thespring is attached to the center bolt by the collar and shear pins, asdescribed hereinbefore.

In assembling the apparatus for use, the sealing cups are rotatedagainst the spring force until they are clear of the coring tubes, andthe center bolt is pushed up in the wrench sleeve until its lower end isflush with the lower end of the outer shell or sleeve, which in turn isflush with the lower end of the coring tubes. The relathe bottom of thecoring tubes. The sealing plugs are held in place by friction againstthe inside walls of the tubes. A

When the coring device has been assembled as described, it is threadedon the bottom of the drill string and lowered in the bore until it restson the bottom of the hole. When the bottom of the shell encounters thehole bottom, the weight of the drill pipe is transferred to the shearpins I IA and IIB which lock the mandrel to the shell. These pins shear,and the weight of the drill string drives the coring tubes into thebottom of the formation.

During the core-taking operation, the sealing plugs keep mud and mudcake out of the lower parts of the coring tubes. As the coring tubesmove downward, the shell is pushed up relative to the mandrel, and atthe same time the cores move the sealing plugs upward in the coringtubes and force the mud above them out of the tubes through the bores 29and outlets 29A. y In the next operation, the drill string is lifted sothat the coring tubes are brought up -in the shell, as shown in Fig. 4.The weight of the shell itself causes it to remain on the bottom of the.hole until the inner shoulder I5 of the mandrel catches against the topof the shell. Before this point has been reached, the coring tubes haveslipped up past the sealing cups sulllciently far to permit the spiralspring to rotate the lower ammasyolelso that'` thecupsareswung-'underthe coring tubes. In other words; the sealing oupssnap intoV position underneath the coring tubesand-are heldlin-:thatposition byf spring tension.

' In;v the next stage ofV the; operation, the drill pine is. lowereduntil itis; certain that the tool is'. again on the bottom of the hole.ThisV lowering'operation anchors-the shell againstv the bot?ntomandmoves. the tubes dow-n-` intothe oupsl so that4 they seat therein(see Fig; 59g. Next, the drill pipe is rotated. The shell? and centerbolt arefvhe'ld stationaryby contact with the bottom, so that therotation of the drill pipe imparted to the sealing nutxthrough` thewrench sleeve causes the sealing nut'- to; thread downwardly on thecenter vboltfandbear against'the upper yoke. This'forces the loweredges: of.` the coring tubesA intothe soft metal gaskets in the-bottomof thesealihg oups as the? upper and lower yokes are brought closertogether. off the tubes are squeezed into their'seats and seal the topsofthe tubes.

At apredetermined wrench force on the Sealing nut, the pins 2o and 26Abetween the wrench sleeve and the mandrel are sheared, sov that nofurther tightening action is permit-ted. rlhis set off shear pins thusprevents excessive pressure from. being exerted upon the sample tubesand the restv of the assembly.

When the drill pipe is rotated, the corin'g' assembly rotates againstVthe tension of the spiral spring,Y and'. as thisv rotation continues,the spring shears the collar away'fromr the centerbolt, this operationtaking' place af-ter the coring tubes have entered thecups. It will benoted that the lower yokeis set onv a bearing and is free to rotateaboutthe center bolt after the spring is: released.

As soon as the shear pins which connect the wrench sleeve to the mandrelhavexbeen released; the coring assembly assumes the position shown inFig. 5-andis ready tocome out of the' hole.

After the coring device hasl been withdrawn to the surface, it isdetached from the drill string. Thereafter the lower endof the outershell is removed; the upper yoke is detached from the mandrel; andthetubes with thesealing'assembly proper are withdrawn from theY apparatusand taken to the laboratory or elsewhere for" tests. Thusv withdrawn,the assembly; in. addition to the tubes containing the cores,includes.thc upper and lower yokes, the sealing plugs; the sealing cupsand the center bolt.V This assembly is light enough to be easilyhandled.

In the' laboratory, the usual'testsiupon the. cores are run' with thevassurance that the results will not be vitiated by contamination of' thecore samples or leakage therefrom'.

To summarize the movements in the sampling operation just described. thestern with theV corihg eqm'pment attached is lowered until the latterrests onthe bottom of theY hole. Some rotation during the loweringoperation is permissible. if desired, andA circulation to the bottomofthe hole is possibleat anytime.

' In' the second phase of' the operation, all or part of thel weight ofthe drill string is set on the bottom of the hole in order to. causeIthe core tubes topenetratev the formation.

In the third stage of the operation, the drill string'is raised untilthe cori'ng'device is offbot.- tom. This permits the sealing cups torotate into sealing position.

In the fourth operation, the-tool is again set on the bottom, and: thedrill pipe is rotated or40 turns to-cause the'yo'kesv to move closertogether At-th'ezsame time the plugs in the top Lil) and`sealupperand?lower' endsiof' thefcoring tubes lI-he fifth stagev of thev operation ismerely the withdrawal off the drill-l string and! theremoval of thesamples in the oori'ng'tubes.

1. In apparatus for attachmentto the bottom of a drillstern for taking aforma-tionsani-plein the bottom of a drill hole, the combination whichcom-prises a mandrel mountable onv the bottom or the stem in alignmenttherewith, a shell sliolalcrly4A mounted upon theV mandrel, ruptura-blemeans initially connecting mandrel and shell toprevent' such sliding; acore barrel? mounted onY the'bottom of the mandrel and having an'4 openlower cutting end, and a closure member mounted on theshell and?vadapted to close thee lower end of' thecore barrel' when the mandrel isslidupwardfwitr respect" tothe shell.

2. In apparatus for attachment to the bottom. of a drill stem fortakingy a formation sample-in the bottom of a drill hole, thecombination which comprises a. mandrel mountable on theA bottom or' thestem in alignment therewith; a shell sllid-l ably mounted upon themandrel, a core barrel mounted: on the bottom of the mandrel and haveingy an open lower cuttingend and also-an open. upper end, a closuremember mounted onthe shell and adapted to close the lowerend of the corebarrel when the mandrelfis slid upward' with! respect to the shell, anda sealing plugI slida'ble in the borey of the core barrel.

3. In apparatus for attachment' toV thelbottomi of a rotaryv drill stemfortak-ing a formation sample in the bottom or adrill' hole, theconrbination which comprisesY a mandrel' mountable? on the bottomof thestem in alignment' there wth, av shell slidably-mounted' uponthemand'rel a core barrel mounted on-thebottomof' the man--l drel andhaving an open lower cutting endl and also an open upper end, avclosureu member mounted on the shell and adapted to closethe' lower endof the corev barrel when-` the mandrel is slid upward with respectvtothe shell; av seal"- ing plugslidable-in thebore of the barrel, a'seat for the plug adjacent the topV 0I" the barrer, and clamping means'actuated by" rotating the drill'l stem'Y for pressing thev closure.member against said lower end.

4-, Apparatus according to cl'aim- 3 provided with a- Valve in the plugwhich is seated when a core is' pushed upwardly in the barrel.

5. In apparatus for attachment tothe lmttonrk of a rotary drill stem fortaking a formation sample in the bottomY ofl a dril'li hole, the comebi'nationI which comprisesa mandrel; mountable? on the bottom of thestern in alignment therewith, a shell slidably mounted upon the mandrel;a core barrelmounted onthe'bottom of' the man.- drel and having an openlower cutting' end). a closure member mounted on the shell and, adaptedto closev the lower. end' of" the core barrel when the" mandrel is slidupward' with respect'. to the shell, a threaded bolt attachedY to theclos'- ure member and extending up into.- a. wrench. bore ofnon-circular cross section on the. axis. of. the mandrel, a nut slidablealong the. bore butf rotatable thereby and., threaded; on the boli-l, anupper yoke attached to the barrel. and a. lower:v yoke attached to the.closure member with. the bolt arranged to press the two yokes. togethervwhen the nut is rotated, thereby pressing, the closure member againstthe lower endf of. the barrel.

6. Apparatus according to. claim.. 5. provided.: With a wrench sleeveof' cylindrical section mounted in a bore in the mandrel and containingthe wrench bore, and shearable means connecting the wrench sleeve to themandrel.

7. In apparatus for attachment to the bottom of a rotary drill stem forpunching out and recovering a sample from the bottom of a drill hole,the'combinaton which comprises a mandrel mountable on the bottom of thestem in alignment therewith, a sleeve mounted around the mandrel andslidable and rotatable with respect to the mandrel, rupturable meansinitially axing the sleeve to the mandrel, at least one core barrelmounted on and below the mandrel in alignment therewith, and having yanopen lower cutting end and an open seat at its upper end, a sealing plugslidable upward in the core barrel to abut the seat, a closure membermounted on the sleeve to swing on an axis extending in the direction ofthe drill string to seal the lower end of the core barrel when it andthe mandrel have slid upward sufficiently with respect to the sleeve, aspring for so moving the closure member and clamping means actuatedthrough rotation of the mandrel and adapted to press the closure memberupwardly against the bottom of the core barrel.

8. In apparatus for attachment to the bottom of a rotary drill stem forpunching out and recovering a sample from the bottom of a drill hole,the combination which comprises a mandrel mountable on the bottom of thestem in alignment therewith, a sleeve mounted around the mandrel andslidable and rotatable with respect to the mandrel, rupturable meansinitially axing the sleeve to the mandrel, an upper yoke attached to themandrel, at least one core barrel mounted on and below the mandrel inalignment therewith, and having an open lower cutting end and an openseat at its upper end, a sealing plug slidable upward in the core barrelto abut the seat, a closure member mounted on a lower yoke attached tothe sleeve to swing on an axis extending in the direction of the drillstring to seal the lower end of the core barrel when it and the mandrelhave slid upward sumciently with respect to the sleeve, a spring for somoving the closure member, a threaded bolt passing through both yokesand extending up into a wrench bore of non-circular cross section on theaxis of the mandrel, and a nut slidable along the bore, but rotatablethereby and threaded on the bolt above the upper yoke, the bolt andyokes being so arranged that rotation of the mandrel causes the nut topress the yokes toward each other.

9. In apparatus for attachment to the bottom of a rotary drill stem fortaking a formation sample in the bottom of a drill hole, the combinationwhich comprises a mandrel mountable on the bottom or the stern inalignment therewith, a shell slidably mounted upon the mandrel, a corebarrel mounted on the bpttom of the mandrel and having an open lowercutting end, a closure member adapted to close the lower end of the corebarrel when the mandrel is slid upward with respect to the shell, andclamping means actuated by rotating the drill stem for pressing theclosure member against said lower end, said clamping means comprising athreaded bolt attached to the closure member and extending up into abore of non-circular cross section in the mandrel on the axis thereof, anut of corresponding cross section slidable in the bore and threaded onthe bolt, an upper yoke attached to the barrel below the bolt, and alower yoke attached to the closure member, the two yokes being soarranged that they are pressed toward each other by rotation of the nuton the bolt.

DONALD M. SMITH.

REFERENCES CITED The following references are' of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,617,659 Whinnen Feb. l5, 19272,216,962 Sewell Oct. 8, 1940 2,238,609 Sewell Apr. 15, 1941 2,373,323Macready Apr. 10, 1945

